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Using a tunnel ram on a Ford is fairly common to clear the distributor.

With the availability of 12-71 and 14-71 cases new or used, why would anyone go to the trouble of welding two together? You could buy a used up case from a drag racer and still have plenty of umph for a street car.

It's my car he's asking about. Why weld two 6V71's together? Because it would make a really big blower. the 8, 10, 12 71 aftermarket blowers are 1 inch longer than a 671 per 2 number add, ie an 871 is long inch longer than a six and a 1071 is two inchs longer. A 671 is just under 15 inchs long, a 6V71 is just under 12 inchs long. Therefore 2 x 6v71 would be almost 24 inchs long, ie about the same as a 2471. So as well as being massive, It adds to the freak value of the car. Car will be running 3 x 660 centre squirters, same reason, cause I can and cause I'm a freak.

It's my car he's asking about. Why weld two 6V71's together? Because it would make a really big blower. the 8, 10, 12 71 aftermarket blowers are 1 inch longer than a 671 per 2 number add, ie an 871 is long inch longer than a six and a 1071 is two inchs longer. A 671 is just under 15 inchs long, a 6V71 is just under 12 inchs long. Therefore 2 x 6v71 would be almost 24 inchs long, ie about the same as a 2471. So as well as being massive, It adds to the freak value of the car. Car will be running 3 x 660 centre squirters, same reason, cause I can and cause I'm a freak.

Freak, yes. Typist no. Reading that was like talking to my 10 year old nephew!
I get what your saying, it would be really wild. If your going for show, then great. If your going racing i think is probably a poorly conceived waste. I'm not sure why, but i don't think it will perform very well. May well make too much boost or heat.

Too much boost or heat? Can't see an issue with either. Boost is set by pulley raio . Since to combined size of the blowers make 654ci per revolution then its just a matter of underdriving to achieve the desired boost. As for heat, since the blower will be spinning slow due to the underdriven nature, then heat should be less of an issue than using a normal sized blower. I am considering putting the blowers back to back before welding and leaving a set of gears at each end of the blower to maintain them in the correct timing and stop then from untwisting due to the length. Any thoughts on this? I understand it an "out there" idea but that is part of the point. Hot Rodding isn't about building a mass producted vehicle but rather an individual piece of "automotive art." The car may see some strip time, but it is not a drag car. I will also only weld the blowers end for end if I am sure it will work, which is why I'm after peoples input. Otherwise I will stick with the 8V71 I already have. (The car will also be running multiple nitrous systems) Yes I am a Freak, but not a fool.

I understand your point of having something different. I run a Dodge dragster because everyone else has a belly button chevy.

This is what Id would do in your position. Drive the front blower off the belt like normal. Put the back blower on backwards. Modify the end plates to spine them together. I would mount them back to back rather than welding. You could easily build a plenum to mount the 3 carbs. Consider using something besides the center squirts. Those are drag race carbs and are not street friendly.

Too much boost or heat? Can't see an issue with either. Boost is set by pulley raio . Since to combined size of the blowers make 654ci per revolution then its just a matter of underdriving to achieve the desired boost. As for heat, since the blower will be spinning slow due to the underdriven nature, then heat should be less of an issue than using a normal sized blower. I am considering putting the blowers back to back before welding and leaving a set of gears at each end of the blower to maintain them in the correct timing and stop then from untwisting due to the length. Any thoughts on this? I understand it an "out there" idea but that is part of the point. Hot Rodding isn't about building a mass producted vehicle but rather an individual piece of "automotive art." The car may see some strip time, but it is not a drag car. I will also only weld the blowers end for end if I am sure it will work, which is why I'm after peoples input. Otherwise I will stick with the 8V71 I already have. (The car will also be running multiple nitrous systems) Yes I am a Freak, but not a fool.

For the record, i love hotrods, and i'm not trying to dissuade you from doing something unique or crazy. I understand wanting something unique (i wanted to build the Gottlieb Big Red camaro when i was a kid, before i ever heard about it). Like i said i can't tell you why, i read the Corky Bell supercharging book, and i seem to remember too big of a supercharger doesn't work well. Maybe because you lose efficiency at too low of a rotor speed? Maybe too much boost at very low rpm?? i don't know. Why dosen't anyone run a 14-71 on a street car? or even most drag cars? What is the reason?

Anyhow, i think the idea of putting them back to back with a spline connection would work better than welding the cases. You could more easily service them, since they are mostly still off the shelf blowers. If you weld and modify the rotors then when you need a part you have the expense and time of custom making the part. If you have an adapter that couples them, you can use more off the shelf parts. Either way, please post pics as the project progresses.

Keep in mind that the number designation of the blower is the engine it was meant for. It is not swept volume. In other words, a 6V71 doesnt displace 426 ci of air on a single revolution.

Another option would be to have the second blower mounted for "show" but only have the front blower functional. Then you would have the advantage of being able to use existing tuning data. Not having to reinvent the wheel would make things less frustrating when it came time to drive it down the street. One blower would still provide a big kick in the seat when the light goes green.

Hi. Thanks for the input. The 654ci quoted is the swept vulome for 2 6V71 blowers as per the chart in Pat Ganahl's book "Street Supercharging". A standard 6/71 is 411ci per rev so its roughly 60% bigger again (not twice the size cause the V series blowers are shorter). There are a couple of reasons for not running a 14/71, firstly in New Zealand (where I am) there is not really a supply of cheap x race units and the buy new option is outside the price range, secondly I like the idea of an odd setup (obviously) and this appeals to me as I have never seen it done before. Running them side by side has been done a few times, as someone else posted photos, and closer to home, Castlemaine Rod Shop in Australia did one (same guy that put a Rolls Royce Merlin in a 55 Chev) Also one top of another has also been done (Silver Bullet Mustang by Gary Myers in Australia and a T Bucket here). Also, side by side or one on top both means two drive snouts.
I'm liking the idea of coupling them together with one drive, this is what detroit did so it can be done. Thanks for the input, I do appreciate the feedback and different points of view, the more people that put their two cents in, the more options people come up with the more chance I have of ending up with the best solution.
As for the 660's. I had thought that they were a good half way point between vac sec and double pumpers? Also, cause they have no clutter on one side, they could be mounted sideways and quite close together, which was my first call when I was looking at a single 8V71 and three carbs. Once again, doing it cause I hadn't seen it done. I have a mate running twin 1150's on a 671 blown 468 so figured 3 x 660 was still smaller than 2x1150. Still open to peoples point of view as I have not run these carbs myself. A consideration, this is a very small car, (under 1000kg? 2200lbs?) running 22.5inch quicktimes (yes it is getting wheelie bars). Maybe I could run 4x450 vac sec?
Thoughts anybody?

Forget the 660s. They dont transition from idle to WOT very well. They are made to be wide open at the starting line and stay that way until the finish line. Youre going to end up with way too much cfm for a street car. You do want it to be a pleasure to drive right? If youre set on three carbs go for the 450s, or go to a bigger carb and disable the secondaries for driving. Yet another option would be a pair of Hilborn 3 port (shorter than 4s). Those would be easily converted to EFI and still maintain the hotrod look. How about a herd of 2GCs or Webers?